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Full Discussion: dd command
Operating Systems Solaris dd command Post 99966 by Perderabo on Wednesday 22nd of February 2006 04:39:10 PM
Old 02-22-2006
Some day I will benchmark a few runs of dd and find the optimal setting, if there is one. I have only dd'ed magnetic disks. Never dd'ed a cd-rom, let alone a dvd. So I'll stay with what I know. Use the rdsk style device, not the dsk so the data goes to straight your data segment (not via the buffer cache). The rdsk driver has to read whole sectors. If you ask for a piece of a sector, it may not work. Or it may read a sector and discard what you don't want. I stay with a multiple of 1024. Bigger is better than tiny. But after a point, the advantage starts to taper off. 1 MB is the smallest size I would consider trying. I will want to mentally estimate how much is left, etc...so no screwball sizes. I wind up with N * (1 MB) where N is some small integer. 10 MB seems like a nice round number. We have one bad spot on the disk. I expect dd to fail when it gets there. I will restart it on the next 10 MB chunk. So I have doomed myself to having a 10 MB hole in my disk. That is pretty much my thought process as I picked my blocksize.

It would be a disaster to pick a buffer size so large that box starts to page. I have plenty of memory on this box, so no problem there.
 

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LEARN ABOUT MINIX

cmdk

cmdk(7D)							      Devices								  cmdk(7D)

NAME

       cmdk - common disk driver

SYNOPSIS

       cmdk@target, lun : [ partition | slice ]

DESCRIPTION

       The  cmdk  device  driver  is  a  common interface to various disk devices. The driver supports magnetic fixed disks and magnetic removable
       disks.

       The block-files access the disk using the system's normal buffering mechanism and are read and written  without	regard	to  physical  disk
       records. There is also a "raw" interface that provides for direct transmission between the disk and the user's read or write buffer. A sin-
       gle read or write call usually results in one I/O operation; raw I/O is therefore considerably more efficient when many bytes are transmit-
       ted. The names of the block files are found in /dev/dsk; the names of the raw files are found in /dev/rdsk.

       I/O  requests  to the magnetic disk must have an offset and transfer length that is a multiple of 512 bytes or the driver returns an EINVAL
       error.

       Slice 0 is normally used for the root file system on a disk, slice 1 as a paging area (for example, swap), and slice 2 for backing  up  the
       entire fdisk partition for Solaris software. Other slices may be used for usr file systems or system reserved area.

       Fdisk partition 0 is to access the entire disk and is generally used by the fdisk(1M) program.

FILES

       /dev/dsk/cndn[s|p]n     block device (IDE)

       /dev/rdsk/cndn[s|p]n    raw device (IDE)

			       where:

			       cn	controller n

			       dn	lun n (0-7)

			       sn	UNIX system slice n (0-15)

			       pn	fdisk partition(0)

       /kernel/drv/cmdk        32-bit kernel module.

       /kernel/drv/amd64/cmdk  64-bit kernel module.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Architecture		     |x86			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fdisk(1M), mount(1M), lseek(2), read(2), write(2), readdir(3C), scsi(4), vfstab(4), attributes(5), dkio(7I)

SunOS 5.10							    9 Oct 2004								  cmdk(7D)
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